1. Field of the Invention
The present invention relates to a scanning device, and more specifically, to a scanning device capable of calibrating the step angle errors of a motor.
2. Description of the Prior Art
Desktop scanners are very popular computer peripheral devices. They are used to scan documents to generate corresponding image data. In addition, scanners can provide extra functionality. For example, a scanner may be used to send image data as fax image data to other facsimile devices through a phone line, to other people in an e-mail format through a network, or to a printer for copying. As the scanning technology progresses, the quality requirements for scanners turns more and more rigid as well. It is therefore an important issue to prevent scanning errors caused by errors of either the hardware or the software of the scanner.
Please refer to FIG. 1 of a schematic diagram of a scanner 10 according to the prior art. As shown in FIG. 1, the scanner 10 includes a housing 12, a transparent platform 14 installed on the housing 12 for a document 20 to be placed on, and a scanning module 16 moveably installed inside the housing 12 for scanning the document 20 and generating an corresponding image of the document 20. The scanner also has a step motor 18, installed inside the housing 12 and physically and electrically connected to the scanning module 16, for driving the scanning module 16 step-by-step to scan the document 20.
Theoretically, ideal step lengths of the scanning module 16 generated by one-step-forwards motions of the step motor 18 are all the same. Each ideal step length equals to a quotient of a distance traveled by the scanning module 16 driven by one complete rotation of the step motor 18, divided by the number of the steps traveled by the step motor 18 during the complete rotation. Unfortunately, a step angle error of the step motor 18 caused by manufacturing errors frequently leads to different step lengths of the scanning module 16 generated by one-step-forwards motions of the step motor 18.
Please refer to FIG. 2a and FIG. 2b, which respectively represent a document to be scanned and an image generated after the scanner 10 scans the document according to the prior art. As shown in FIG. 2a, the document to be scanned includes three parallel lines 21, a distance 22 between the first and second lines 21 being equal to a distance 24 between the second and the third lines 21. Due to the step angle error of the step motor 18, the image generated after scanning the document is slightly different from an actual image of the document. As shown in FIG. 2b, a distance 26 between the first and second lines 21 on the generated image, and a distance 28 between the second and the third lines 21 on the generated image are not equal to the distance 22 between the first and second lines 21 on the actual image of the document and the distance 24 between the second and the third lines 21 on the actual image of the document. In other words, the step angle error of the step motor 18 leads to a scanning error of the scanner 10. In addition to the step angle errors in the step motor 18, slight angle errors of spokes also frequently occur in servomotors due to manufacturing errors and lead to errors of images generated by scanning. The higher the resolution of the scanner is, the more conspicuous and intolerable the error of the generated image caused by the angle error is.
It is therefore a primary objective of the claimed invention to provide a scanning device for calibrating step angle errors of a motor.
According to the claimed invention, a scanner comprises a housing, a transparent platform, a scanning module, a motor, and a calibration paper. The transparent platform is installed on the housing for a document to be placed on. The scanning module is moveably installed inside the housing for scanning the document. The motor is installed inside the housing for driving the scanning module. The calibration paper is installed at a front end of the housing and has a graph for calibrating step angle errors of the motor.
It is an advantage of the claimed invention that the scanner includes the calibration paper. The scanner scans the graph on the calibration paper before scanning the document to obtain the ideal step length of the scanning module generated by the step motor. In addition, the comparison table disclosed in the claimed invention stores the ideal step length and the actual step length of both the scanning module and the step motor. Thus the scanning module calibrates the image generated by scanning the document according to the distance between the graph and the front end of the transparent platform 54, the actual step lengths and the ideal step lengths of the scanning module 56. Consequently, the accuracy of the scanning is significantly improved.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment, which is illustrated in the multiple figures and drawings.